In mobile wireless communication, a channel state (wireless characteristics) of a radio channel between a base station and a wireless terminal changes according to a time, and changes according to a frequency, too. Hence, channel states of a downlink radio channel from the base station to the wireless terminal and an uplink radio channel from the wireless terminal to the base station are estimated.
When the base station and the wireless terminal communicate by way of time divisional duplex, the channel states of the uplink radio channel and the downlink radio channel can be estimated to be equivalent.
However, the channel states of the uplink radio channel and the downlink radio channel which can be estimated to be equivalent are channel states of the radio channel in air between an antenna of the base station and an antenna of the wireless terminal. Meanwhile, the radio channels estimated by the base station and the wireless terminal include response characteristics (transfer function) of a wireless transmission/reception circuit between a channel estimator and the antenna, and therefore the channel states of the uplink radio channel and the downlink radio channel are not actually estimable as being equivalent in some cases. Hence, the wireless transmission/reception circuit is calibrated to able to estimate that the channel states of the uplink radio channel and the downlink radio channel are equivalent.    Patent Document 1: Japanese Laid-open Patent Publication No. 2013-534380    Patent Document 2: International Publication Pamphlet No. WO 2011/155360    Patent Document 3: Japanese Laid-open Patent Publication No. 2011-199850    Patent Document 4: Japanese Laid-open Patent Publication No. 2013-509082    Non-Patent Document 1: K. Nishimori, K. Cho, Y. TAKATORI, and T. Hori, “A Real-Time Calibration Method of Adaptive Arrays for TDD Systems” A⋅P99-3, IEICE technical report, pp 17-22, April 1999.    Non-Patent Document 2: Y. Nouda, Y. Hara, Y. Yano, H. KUBO, “An Antenna Array Auto-Calibration Method with Bidirectional Channel Measurement for TDD Systems”, RCS2008.12, IEICE technical report, pp 69-74, May 2008.    Non-Patent Document 3: H. Fukuzono, et al, “Weighted-combining calibration for implicit feedback beamforming on downlink multiuser MIMO systems,” PIMRC 2013, June 2013.    Non-Patent Document 4: F. Huang, Y. Wang, J. Geng, D. Yang, “Antenna mismatch and calibration problem in coordinated multi-point transmission system,” IET Commun, 2012, Vol. 6, Iss 3, pp. 289-299.
When a base station is connected to a plurality of transmission and reception points, and the plurality of transmission and reception points communicate with a wireless terminal in a coordinated manner, radio signals received by the wireless terminal from the plurality of transmission and reception points are preferably equivalent. Hence, it is may be demanded to accurately calibrate the base station connected to the plurality of transmission and reception points.